1. Field of the Invention
This invention relates to a horizontally articulated robot, and more particularly to increase of the speed of operation of its horizontal arm and to improvement of the reliability in operation of the same.
2. Prior Art
FIG. 1 shows a conventional industrial robot similar to an industrial robot which has been disclosed by Japanese Patent Application (OPI) No. 211889/1983 (the term "OPI" as used herein means an "unexamined published application"). In FIG. 1, reference numeral 1 designates a base body; 2, a lift shaft provided in the base body 1; 3, a horizontal arm provided on the side of the base body one end portion of which is pivotally mounted on the upper end portion of the base body 1 (hereinafter referred to as "a first horizontal arm 3" when applicable); 4, a first drive unit including an electric motor and a speed reducer, the drive unit being mount on the upper end of the lift shaft 2 to turn the first horizontal arm 3; 5, a horizontal arm provided on the side of work (hereinafter referred to as "a second horizontal arm 5" when applicable), the horizontal arm being pivotally coupled to the outer turning end of the first horizontal arm 3; 6, second drive unit including an electric motor and a speed reducer, the drive unit being provided at the outer turning end of the first horizontal arm 3 to turn the second horizontal arm; 7, an operating hand pivotally coupled to the outer turning end of the second horizontal arm 5; 8, a third drive unit including an electric motor and a speed reducer, the third drive unit being provided at the outer turning end of the second horizontal arm 5 to turn the operating handle 7; 9, a cable inserted into the base body 1 with its one end connected to the first drive unit 4 provided for the first horizontal arm 3; 10, a cable inserted into the base body 1 with its one end connected to the second drive unit 6 provided for the second horizontal arm 5; 11, a cable inserted into the base body 1 with its one end connected to the third drive unit 8 provided for the operating hand 7; and 12, a holder supporting the cables 10 and 11 at the middle.
The conventional industrial robot is constructed as described above. Its hand 7 is positioned by operating the robot as follows: The lift shaft 2 is operated to set the first horizontal arm 3 at a desired level. The first drive unit 4 is energized through the cable 9 to turn the first horizontal arm 3 to be set at a desired position. The second drive unit 6 is energized through the cable 10, to swing the second horizontal arm 5 to be set at a desired position. Similarly, the third drive unit 8 is energized through the cable 11, to turn the hand 7 to cause the latter 7 to take a predetermined posture. With the hand 7 thus positioned, a predetermined operation is carried out. Thereafter, the drive units 4, 6 and 8 are energized again, to perform the next operation.
In the above-described industrial robot, the heavy drive units 4, 6 and 8 are provided at the ends of the first and second horizontal arms 3 and 5, and are energized through the cables 9, 10 and 11. In order to operate the first and second horizontal arms 3 and 5 at high speed or at high acceleration or deceleration speed, it is necessary to increase the output power of the drive units 4, 6 and 8. However, to do so is to increase the weight of the drive unit. Therefore, it is rather difficult for the conventional industrial robot to increase the speed of the horizontal arms. Furthermore, because the robot is operated through the cables 9, 10 and 11, it is essential to prevent the occurrence of troubles due to the breakage or disconnection of the cables.